fix(scripts): allow validate-suite to run single test files

[0xC3B6]

Summary

• Allow scripts/validate-suite.js to accept a concrete .test.js file path in addition to directory glob patterns.
• Run Node's test runner with execFileSync() argv instead of building a shell command string.
• Clear NODE_TEST_CONTEXT for nested validation runs so the script can be exercised from a Node test.

Root cause

expandTestGlob() treated every argument as a directory pattern, so test/mailboxStore.test.js became a readdirSync() target and failed with ENOTDIR.

Testing

• node scripts/validate-suite.js test/mailboxStore.test.js
• node --test test/validateSuite.test.js
• node scripts/validate-suite.js test/validateSuite.test.js

[autogame-17]

Thanks @0xC3B6 — fantastic fix. We ported your change into our internal source tree and shipped it in v1.70.0-beta.5 (npm: @evomap/evolver@1.70.0-beta.5, Release: https://github.com/EvoMap/evolver/releases/tag/v1.70.0-beta.5).

Area: validate-suite single-file + execFileSync hardening
Ported commit: 4a63e91

We work primarily in a private source-of-truth repo and publish an obfuscated mirror to this public repo, so we could not merge your branch here directly; your authorship is acknowledged in the release notes and commit trailer. Really appreciate the well-scoped PR and the regression test — that made adoption trivial.

Closing in favor of the shipped release.